1. Field of the Invention
The present invention relates to a nonwoven fabric carrying powder materials affixed thereon, i.e., a powders-affixed nonwoven fabric, a process for manufacturing the same, and a sheet material comprising the same.
2. Description of the Related Art
A fibrous material carrying powder materials affixed thereon is disclosed in, for example, Japanese Unexamined Patent Publication No. 63-135550 wherein a fibrous material carrying powdery binding agents is disclosed. However, the fibrous material is a starting material for a glassfiber-reinforced plastic molding, and fibers having a single fiber diameter of 5 to 20 xcexcm and a fiber length of 4 to 25 mm as the glass fibers. Thus, the powder materials having small particle diameters are not firmly bonded, but easily drop when the fibrous material is vibrated or shocked. Further, Japanese Unexamined Patent Publication No. 7-313863 discloses an air-mixing method of reinforcing fibers and resin powders by a gas stream, for preparing a preform of a fiber-reinforced plastics. However, the reinforcing fibers used are apparently thick and long, and thus, the method has disadvantages same as the above method.
Further, methods for bonding powder materials to a nonwoven fabric were known. For example, there was a method for fixing powder materials by sandwiching the powder materials between fiber webs, and needle-punching the fiber webs to physically entrap the powder materials between fibers. Further, there was a method for enhancing the bonding by sandwiching the powder materials between fiber webs containing heat-sensitive adhesive fibers, and adhering the powder materials and the fibers, and the fibers to each other. However, there was a disadvantage in that small powder materials having an average particle diameter of about 50 xcexcm or less are liable to fall, when the nonwoven fabric is vibrated or shocked, and therefore, the nonwoven fabric can merely bond relatively large powder materials having an average particle diameter of more than 50 xcexcm.
A method for enhancing holdability of the powder materials having small particle diameters, using a fiber web having a denser structure was known. The method was a wet-laid method wherein such powder materials were deposited together with fibers. However, there was a disadvantage in that slurry used in the wet-laid method contains surface-active agents or sizing agents which cover the surfaces of the powder materials, and thus, inherent functions of the powder materials are lost.
The inventors of the present invention engaged in intensive research to remedy the above disadvantages of the prior art, and to provide a powders-affixed nonwoven fabric from which fine powder materials hardly drop, and which can express inherent functions thereof, and a process for manufacturing the same. As a result, the inventors found a means for solving the above problems, more particularly, that a method other than a wet-laid method must be used in order to maintain and express the inherent functions of the powder materials, and a falling of the powder materials from the nonwoven fabric can be prevented by dispersing fine short fibers having a particular thickness or less and a particular length or less to surround the powder materials by the fine short fibers, preferably entangle the fine short fibers as a spider""s web, and narrow gaps between the fine short fibers.
The present invention is based on the above findings.
Other objects and advantages of the present invention will be apparent from the following description.
In accordance with the present invention, there is provided a powders-affixed nonwoven fabric prepared from a fiber web comprising fine short fibers having a fiber diameter of 4 xcexcm or less and a fiber length of 3 mm or less in a dispersed state in the powders-containing fiber web, the powders-containing fiber web being formed by a method other than a wet-laid method.
When an average particle size of the powder materials in the powders-affixed nonwoven fabric is 50 xcexcm or less, functions of the powder materials can be expressed to a maximum degree. Further, when a mass ratio of the fine short fibers with respect to a whole mass of the powders-affixed nonwoven fabric is 1 to 40 mass %, functions of the powder materials can be expressed to a maximum degree, because an amount of the powder materials becomes large. When an adhesion rate of substances adhered to the powders-affixed nonwoven fabric is 0.5 mass % or less, functions of the powder materials are not affected by the substances adhered to the powders-affixed nonwoven fabric.
The inventors of the present invention also found that when aggregates of fine short fibers or a group of the aggregates, and/or mechanically dividable fibers capable of generating fine short fibers or aggregates of the mechanically dividable fibers are ejected together with powder materials from a nozzle into a gas by an action of a compressed gas, the aggregates of the fine short fibers or the groups thereof and/or the mechanically dividable fibers or the aggregates thereof are loosed and dispersed, the powder materials are also dispersed, and individual powder materials are entangled by the fine short fibers as in a spider""s web.
In accordance with the present invention, there is also provided a process for manufacturing a sheet material comprising the steps of:
ejecting aggregates of fine short fibers having a fiber diameter of 4 xcexcm or less and a fiber length of 3 mm or less, or a group of the aggregates, and/or mechanically dividable fibers capable of generating fine short fibers having a fiber diameter of 4 xcexcm of less and a fiber length of 3 mm or less, or aggregates of the mechanically dividable fibers, together with powder materials, from a nozzle into a gas by an action of a compressed gas, to thereby divide the aggregates of the fine short fibers or the group thereof into the fine short fibers, and/or divide the mechanically dividable fibers or the aggregates thereof into the fine short fibers, and disperse the resulting fine short fibers and the powder materials;
collecting the dispersed fine short fibers and the powder materials to form a powder-containing fiber web; and affixing the powder materials, while forming a nonwoven fabric from the powders-containing fiber web, and at the same time bonding a layer free of the powder materials, to obtain the sheet material containing a powders-affixed nonwoven fabric.
In accordance with the present invention, there is also provided a sheet material comprising at least one layer of a powders-affixed nonwoven fabric prepared from a fiber web comprising powder materials and fine short fibers having a fiber diameter of 4 xcexcm or less and a fiber length of 3 mm or less in a dispersed state in the fiber web, the powders-containing fiber web being formed by a method other than a wet-laid method.
The sheet material can further contain a layer free of the powder material to thereby prevent the powder materials from falling on at least one surface, and such a layer can more effectively prevent the falling of the powder materials.
In accordance with the present invention, there is also provided a process for manufacturing a sheet material comprising the steps of:
Ejecting aggregates of fine short fibers having a fiber diameter of 4 xcexcm or less and a fiber length of 3 mm or less, or a group of the aggregates, and/or mechanically dividable fibers capable of generating fine short fibers having a fiber diameter of 4 xcexcm of less and a fiber length of 3 mm or less, or aggregates of the mechanically dividable fibers, together with powder materials, from a nozzle into a gas by an action of a compressed gas, to thereby divide the aggregates of the fine short fibers or the group thereof into the fine short fibers, and/or divide the mechanically dividable fibers or the aggregates thereof into the fine short fibers, and disperse the resulting fine short fibers and the powder materials;
collecting the dispersed fine short fibers and the powder materials to form a powder-containing fiber web;
and affixing the powder materials, while forming a nonwoven fabric from the powders-containing fiber web, and at the same time bonding a layer free of the powder materials, to obtain the sheet material containing a powders-affixed nonwoven fabric.